The aetiology of this syndrome is far from clear. Detailed examinations of juvenile pandas with this condition have consistently revealed one or more systemic illnesses during critical growth and developmental stages. Any sickness may lead to an interval of suboptimal nutrition which results in malnutrition, enamel dysplasia and, eventually, stunted growth. We also have anecdotal and unsubstantiated evidence that some animals may recover and develop into reproductively successful individuals, with only minor residual effects, such as dental abnormalities. Others are unable to recover, continue to develop serious chronic medical problems and never reproduce. Although a definitive cause has not been established, infectious disease (e.g. canine distemper, canine parvoviral enteritis or E. coli enteritis) may play a role in inciting this syndrome in juveniles. Baylisascaris infections are generally considered non-pathogenic, but may also influence the health of young, developing giant pandas. Dietary excesses during growth, nutritional deficiencies (including premature weaning) or diet-induced gastroenteritis may cause growth and developmental challenges. Specific dietary problems, such as lactose intolerance or intestinal dysbiosis, may be examples. Causes specific to the dental abnormalities, such as tetracycline administration or fluorosis, should also be considered.

Aside from failing to understand its aetiology, the major concern with Stunted Development Syndrome is its influence on captive population viability. As discussed by Ballou et al. (see Chapter 21) it is essential that every valuable individual reproduce with its most genetically appropriate mate. The finding of a developmental anomaly that occurs after the critical neonatal period illustrates the importance of being vigilant about the health of juveniles. We now know that ensuring that young cubs survive is not enough - rather, the appropriate management of juveniles is essential to assuring long-term health and eventual reproductive success. Although it appears possible to recover the health of some younger animals that are on track for becoming 'stunted', years of reproductive success can be lost, sometimes permanently.

Abdominal effusions (ascites)

An abdominal effusion (fluid accumulation) was detected by ultrasound in 15 of 61 (24.6%) animals examined. All of these were adults (three males, 12 females), and nine had been born in captivity. Amounts measured were generally considered mild to moderate but three pandas (SB 325, 388 and 393) were experiencing severe fluid accumulation surrounding the abdominal organs (Fig. 4.2). Each of these individuals had a visibly distended abdomen and other signs of chronic disease, including decreased body condition, generalised oedema and

abnormal dentition. The cause of the abdominal fluid has not been determined, and ascites has not been reported as a significant medical problem in this species, although occasional ascites episodes have been noted, including in a giant panda maintained outside China (see Chapter 17). Regardless, it should be emphasised that small amounts of ascites appeared unrelated to clinical disease or to reproductive failure.

Dental disease

Dental disease, characterised by broken canine teeth or excessive wear with apparent enamel dysplasia, was not uncommon in the surveyed population. Fractured canine teeth with exposed root canals occurred in 10 of 61 (16.4%) giant pandas (two males, eight females, all adults, with half of these born in captivity). Although radiographs were not taken to assess extent of tooth-related disease, fistulations were absent upon physical examination. However, one individual had a firm swelling at the base of a fractured tooth (Fig. 4.3). For the long-term health of these animals, it will be important in the future to perform endodontic procedures to restore these teeth.

Figure 4.3. Lateral view of the dentition of a 16-year-old male giant panda (SB 305; wild born). The upper left canine is fractured exposing the root canal (white arrow). Above the fractured canine is a hard, bulbous swelling possibly related to the damaged tooth (black arrow). An X-ray unit was unavailable to help determine the nature of this swelling.

Figure 4.3. Lateral view of the dentition of a 16-year-old male giant panda (SB 305; wild born). The upper left canine is fractured exposing the root canal (white arrow). Above the fractured canine is a hard, bulbous swelling possibly related to the damaged tooth (black arrow). An X-ray unit was unavailable to help determine the nature of this swelling.

Another nine giant pandas (14.8%) were experiencing excessive tooth wear, pitting and/or staining compared to counterparts of similar age and sex (Figs. 4.4 and 4.5; Plates IV and V). The most extreme cases involved pandas with enamel loss so severe that the underlying dentin was clearly exposed. This finding led us to suspect that this condition has its origin during early development (see 'Stunted Development Syndrome', p. 70),

Demodecosis

Six of 61 giant pandas (9.8%) had clinical disease associated with Demo-dex sp. skin mites (Fig. 4.6). Diagnosis was made by performing a skin scraping of the affected area followed by microscopic examination (Fig. 4.7). All but one affected panda was an adult, and four had been captive born. The most typical lesions were mild alopecia associated with crusting and swelling of the eyelids. In one case, a 5.5-year-old male (SB 392) had severe, generalised demodecosis with widespread alopecia, erythema, pyoderma and lichenification of the skin.

Ascarid infection

Baylisacaris (Ascaridia) schroederii is a well-known parasite of the giant panda (Qiu & Mainka, 1993; Mainka, 1999). Although it is not uncommon for pandas to pass whole adult worms in the faeces or vomit, corresponding ova are infrequently detected in routine microscopic examinations of faecal samples. Using routine faecal flotation techniques, we detected ascarid ova in only a single juvenile female (SB 477; 1.5 years old). We are confident that ascarids are present in the captive environment of the giant panda. However, the prevalence and, more

Figure 4.5. Close-up of newly erupted canine teeth and lower third incisor of an 18-month-old giant panda male (SB 454). Defects in the enamel (including staining and pitting) can be observed.) (See also Plate V.)

importantly, the impact of this parasite on growth and development of the young giant panda remain unclear and deserve more research attention.

Testicular hypoplasia

Two cases of asymmetrically sized testes were encountered in normal-sized giant pandas during the Survey (SB 323 and 345). From histories, it was possible that the testicles developed normally and then decreased in size (atrophy) or at least in one case (SB 323) became hypoplastic (see Chapters 7 and 16) (Fig. 4.8; Plate VI). In both cases, the testes

Figure 4.8. A 12.5-year-old male giant panda (SB 323) with a hypoplastic left testicle. The ultrasound images show the normal architecture and size of the right testis versus the hypoechoic condition of the smaller left testis. (See also Plate VI.)

were completely descended and in the normal location in the scrotum. Another male, with Stunted Development Syndrome (SB 356), had bilaterally juvenile testes despite being 8.5 years old (see Chapter 7).

Squamous cell carcinoma

Studbook 305, an adult male (originally wild born) was examined for the Survey at the China Conservation and Research Centre for the Giant Panda (Wolong Nature Reserve) in 2000. This individual had recently been moved from another institution, in part because of its serious health condition - an extremely large (approximately 50-cm diameter) open wound on the central back area. The veterinary team suspected skin cancer as the cause, and biopsies from the site confirmed a locally invasive squamous cell carcinoma. Prognosis for such an extensive lesion was deemed poor. This giant panda was treated sup-portively but died several months later. Despite the illness, semen quality was excellent at the time of the Biomedical Survey and, prior to his death, sperm from this male were used to artificially inseminate SB 432 who later produced a surviving female cub (SB 512) (see Chapter 20).

Uterine/cervical infection

During the ultrasound examination of each female, the focus was largely on identifying and evaluating reproductive tract status. In most cases the uterine body was readily identified through the bladder 'window' or directly by rectal probe (Fig. 4.9). Giant pandas SB 374 and SB 404 had evidence of fluid present within the uterine body as revealed by a hypoechoic line in the uterine lumen when viewed longitudinally (Fig. 4.10). The 6.5-year-old SB 404 also had a history of 'weak' oestrus and had never conceived despite having mated and being artificially inseminated. Direct vaginal examination indicated the presence of a cloudy discharge at the cervical os. Cytology and biopsy of the cervix revealed a suppurative cervicitis. The uterus was flushed with a solution of saline and gentamicin and the animal treated with a three-week course of oral ampicillin. That same breeding season, she displayed normal oestrus, mated and produced a male cub (SB 518).

Figure 4.9. Ultrasound image obtained with a rectal transducer of a normal urinary bladder (b) and uterine body (white arrows). The uterus is free of luminal fluid as indicated by the hyperechoic endometrial line (black arrow). The diameter of this portion of the uterine body is cm.

Figure 4.10. Ultrasound image obtained with an abdominal transducer of the bladder (b) and uterus showing a hypoechoic line representing uterine fluid (arrow). This 6.5-year-old female (SB 404) had a purulent cervicitis, which was presumed to be related to endometritis. She was treated with injectable antibiotics and successfully conceived shortly after this image was taken.